Electrosurgical apparatus

ABSTRACT

An electrosurgical apparatus comprises a high frequency generator ( 1 ) with an associated power control system, a handpiece ( 2 ) with means for removably mounting an electrode ( 5 ) therein, and a connection cable ( 3 ) between an output ( 4 ) of the generator and the handpiece. The transfer characteristic of the system provides a substantially true ohmic transfer of loads on the electrode side of the connection cable ( 3 ) to the generator side thereof at or around a predetermined load on the electrode. 
     In order to achieve a fully automatic and optimalized control af power supplied from a cutting electrode, whereby the control is instantly responding, to changes in the electrode load, the electrosurgical apparatus is characterized in that the power control system comprises a driver stage ( 7 ) followed by a reflectormeter ( 9 ) adapted and arranged to sense the generator output ( 4 ). A detector ( 10 ) supplies a detector signal which represents the reflected signal on the output ( 4 ), and the detector signal is communicated to the driver stage ( 7 ) for controlling the gain thereof.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to an electrosurgical apparatus of thetype which is used, in particular by surgeons and dentists, to performincisions and also to stop bleeding.

2. Prior Art

Electrosurgical equipment of the type in question is based on a powergenerator which supplies a high frequency alternating current. Via aconnection cable this current is conducted to an electrode—the so-calledactive electrode—which is replacably mounted in a handpiece. Fordissections the active electrode is usually made of thin metal wirewhich remains cold because of good conductivity, but when the electrodeis advanced through tissue, a local heating is generated in the tissuea. o. because of the electrical resistance of the tissue.

This heating causes a molecular dissolution of the tissue cells sincethe generated heat causes both intra- and extracellular generation ofsteam which bursts the tissue cells, and the result is a well-definedincision in the tissue. How deep this dissolution takes place in thetissue is depending a. o. on the current intensity and on the speed atwhich the electrode is advanced through the tissue. Normally the facesof incision are substantially free of bleeding, and the damages toadjacent tissues are at a minimum.

Because of the restraining effects to bleeding, the equipment can alsobe used specifically to stop bleeding. For that purpose the generator isusually switched to provide a modulated current waveform, and the resultis a deeper coagulation necrosis relative to the electrode which usuallyis ball-shaped for that purpose. The result is an efficient hemostasisin connection with concentrated as well as more diffuse bleeding.

An important benefit of using electrosurgery instead of a scalpel is asubstantially more precise incision and, moreover, the operating fieldremains clean, dry and without bleeding. This is an essential advantagee.g. in connection with the taking of impressions for tooth crowns andbridges, because an impression can be taken immediately after after thatthe necessary incisions have been made, Electrosurgery is alsowell-suited for pre-prosthetic surgery and for paradontal surgery aswell.

In electrosurgery one of the principal goals is to make clean cuts witha minimum of tissue destruction. This requires that the output powerfrom a cutting electrode continously is precisely adapted to the type oftissue and to the amount of issue (the depth of cut) with which theelectrode is in contact. At the same time the output power may at noinstant be larger than necessary, because too large power delivery willresult a.o. in unclean cuts and possibly also in sparkling betweenelectrode and tissue which causes tissue necrosis and therebycomplicates and prolonges the healing proces.

In particular the output power must be effectively and rapidly reducedas soon as a cutting electrode approaches the periosteum or bone tissue.Otherwise, the result would be very painful damages such as periostitis,bone necrosis and sequestration of bone tissue.

In other words, electrosugical equipment of the type under considerationfor making incisions in living tissues must include very efficient meansfor continuous control or dosage of the power supplied by a cuttingelectrode, Moreover, such power control means must respondrapidly—virtually instantly—to changes in the electrical load of theelectrode i.e. the conductivity or susceptance.

The electrical load is to an essential extent determined by two factors,namely the material resistance i.e. the inherent resistance of thetissue, and the conducting area i.e. the area of contact betweenelectrode and tissue (the depth of cut).

Both factors may vary during a cutting operation. If for instance anelectrode which is advanced at constant depth through soft tissue,approaches bone tissue, then there will be a sudden decrease in the loador susceptance experienced by the electrode, because bone tissue has asubstantially higher electrical resistance than soft tissue due to thesubstantially lower contents of liquid in bone tissue. As alreadymentioned a very rapid reduction of the power supplied by the electrodemust take place in such instances, because, otherwise, the result couldbe very painful damages to bone tissue or tooth substances.

If on the other hand the cutting depth of the electrode is suddenlydecreased, then there will also be a sudden decrease in the load orsusceptance due to the decreasing area of contact between tissue andelectrode. The minimum load or susceptance which is zero, at least inprinciples, will occur when the electrode gets free the tissue—and thusis in the air. Again it is very important that the power from theelectrode is decreased very rapidly, because otherwise the result couldbe sparkling and serious burning and destruction of tissue.

In conclusion, it is important that the power supplied by a cuttingelectrode is efficiently and rapidly decreased as soon as the load orsusceptance experienced by the electrode is decreased for one reason oranother.

DK patent No. 149 762 discloses an electrosurgical apparatus of the typeunder consideration and which provides an extremely rapidly andprecisely responding control of the power output from the electrode as afunction of the instant load on the electrode. This control has beenachieved by using impedance matching techniques, and the system ismatched or in tune at one quite specific load impedance which occurswhen an electrode is cutting at maximum depth in soft tissue.

In or immediately around this particular matched condition, the outputpower from the electrode will accordingly be at its maximum, whereas theoutput power will be efficiently and rapidly decreased because ofmismatching in all other conditions i.e. with decreasing depth of cutand/or with increasing electrical tissue resistance.

Thus, impedance matching technique has been utilized to deliberatelymis-match the output stage in such a manner that the oscillationability, and thereby the power output, is reduced as soon as theelectrode load moves away from the particular condition with impedancematching. The result is an automatic and direct regulation in true timeof the power output as a function of the instantaneous load and in sucha manner that the power delivered to the tissue by a cutting electrode,continuously is adapted to the type of tissue and/or to the depth ofcut.

However, in the electosurgical apparatus just described it has been seenthat the regulation range for output power is not sufficiently broad torange—without further measures—all the way from cutting in the tissuesurface without sparkling (minimum load) and up to cutting in full depthwith maximum power (maximum load). It has therefor often been necessaryto compromise either by renouncing on a part of the available maximumpower in return of a completely sparkless operation, or by acceptingsome degree of sparkling in return of availability of the full maximumpower.

OBJECT AND SUMMARY OF THE INVENTION

It is the object of this invention to remedy this drawback of the priorart apparatus by providing an electrosurgical apparatus of the same typewith instantly responding power control based on impedance matchingtechnique, but in which the complete range of regulation is constantlyavailable.

The primary or continuous control of the output power during dissectionstakes place by means of the system known per se and which is based onimpedance matching technique. This control takes place instantly and independence of the instantaneous electrical load on the electrode.

Concurrently herewith the apparatus of the invention is performing acontinuous and automatic adjustment of the output power level, in asmuch as the gain of the driver stage automatically can be controlled todecrease, when the reflectometer is sensing that a major part of theoutput signal is being reflected—that is to say during incisions withsmall depths (low load). Hereby the sparkling can be controlled andefficiently prevented.

Correspondingly, the gain of the driver stage can be controlled toautomatically increase when the reflectometer is sensing that only aminor part of the output signal is being reflected—that is to say duringdeep incisions (high load). Hereby the maximum power can be made fullyavailable when making deeper incisions.

In other words the invention provides an optimized power characteristic,and the power control takes place in a fully automatic manner completelywithout the need of manual adjustments.

The invention will now be described in further details and withreference to the drawing which is a block diagram of an electrosurgicalapparatus according to the invention.

BRIEF DESCRIPTION OF THE DRAWING

As shown schematically in the drawing the apparatus of the inventionincludes a generator part 1, a handpiece 2, and a connection cable 3between the handpiece and an output 4 of the generator part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF INVENTION

The generator part 1 is based on a BP-oscillator 6 which preferably is acrystal controlled, 50 watt generator with an output frequency of 27.125Mhz which is within a free transmission frequency range.

The oscillator 6 supplies a driver stage 7 which preferably is a 5 wattamplifier stage, and in the embodiment shown the driver signal isconducted to a PA-stage 8. In a preferred embodiment the PA-stage 8includes a transformer which is phase splitting the driver sign by 180degrees, and the resulting signal drives a following PA-stage,whereafter the power is combined in a following transformer.

The PA-stage 8 is followed by a directional coupler or a reflectometer 9which is in communication with the output stage 4 which preferablyincludes a low-pass filter for reduction of the radiation of harmonicsbefore the output signal is conducted to an output terminal.

The handpiece 2 includes means for replacably coupling of an electrode 5which usually is a thin wire electrode which can be shaped in variousways in view of the contemplated use. Other more special electrodes mayalso be used e.g. for stopping bleeding.

By use of impedance matching techniques the system is tuned in such amanner that one quite specific electrical load on the electrode 5 willbe transferred to the generator end of the cable 3 by a true ohmictransfer. Accordingly, the system is in tune or matched at thatparticular electrode load, and the power supplied by the electrode isconsequently at its maximum, because the reflected part of the generatoroutput signal is at a minimum.

At every other electrode load the power supplied by the electrode willbe reduced because a bigger part of the generator output signal is beingreflected due to mis-matching.

The result is a continuous, automatic, and instantly responding controlof the power supplied by a cutting electrode in dependence of theinstantaneous electrical load encountered by the electrode.

The reflectometer 9 in the generator part 1 of the apparatus of theinvention is currently sensing the instantaneously reflected part of theoutput signal, and a detector circuit 10 provides a detector signalwhich corresponds to the reflected signal part on the generator output4. The detector signal wil accordingly vary with and represent theinstantaneous load of a cutting electrode.

The detector signal from circuit 10 is utilized to control the gain inthe driver stage 7, and preferably this takes place via a DC amplifier11 designed to adjust or adapt DC level and gain.

Hereby a positive feed back has been provided by means of which the gainof the driver stage 7 is being regulated in dependence of the size ofthe reflected signal on the output which means in dependence of theinstantaneous electrode load.

Accordingly and concurrently with the instantly responding power controlbased on impedance matching technique, there will be an automaticadjustment or setting of the level of the output power, in as much asthe gain in driver stage 7 can be reduced to a desired extent at highvalues of the reflected signal (low electrode loads), whereby the signallevel on the output will be correspondingly lower. The instantlyresponding power control is still going on to a fall extent, butconsequently now at or around the lower or reduced power level.

Correspondingly the gain in driver stage 7 can be appropriatelyincreased at low reflected signal values (high electrode loads), wherebythe signal level on the output will be correspondingly higher. Again theinstantly responding power control continues to a full extent at oraround the higher or increased power level.

The result is an improved and optimalized power control characteristicspanning over au expanded power range which extends all the way fromquite law output powers and up to the maximum power which the generatoris able to supply. Throughout the expanded range the power control isgoing on in a fully automatic manner and with extreme rapidness.

Consequently and without further measures the electrosurgical apparatusof the invention is able to operate without sparkling at quite lowelectrode loads (small depths of cut), and at the same time the maximumpower is available to a full extent for making deep incisions.

1. An electrosurgical apparatus comprising a high frequency generator(1) with an associated power control system; a handpiece (2) with meansfor removably mounting an electrode (5) therein; and a connection cable(3) between all output (4) of the generator and the handpiece (2);wherein the transfer characteristic of the system provides asubstantially true ohmic transfer of loads on the electrode side of theconnecting cable to the generator side thereof at or about apredetermined load impedance on the electrode (5), characterized in thatsaid power control system comprises a driver stage (7) followed by areflectometer (9) adapted and arranged to sense the generator output(4); and in that a detector (10) is adapted and arranged to supply adetector signal representing the reflected signal on the generatoroutput (4), whereby said detector signal is communicated to said driverstage (7) for controlling the gain thereof.
 2. An apparatus as definedin claim 1, characterized in that said detector signal is communicatedto said driver stage (7) trough a DC amplifier (11) arranged to adjustDC level and gain.